The effects of development and regression of atherosclerosis on the hemodynamics of the aorta and leg arteries will be studied in two species of monkey and in man. Non-invasive and invasive techniques will be used in the monkey studies; and non-invasive techniques in man to obtain pulse transit times, velocities, and frequency components of the cardiac ejection pulse as it travels down the aorta and leg arteries. These data will be correlated with anatomical and biochemical data obtained at critical points in the study. These studies should provide a link between physiology and pathology in atherosclerosis and it may also lead to a non-invasive method of evaluating atherosclerosis in man. The time lag between the onset of hypercapnea and regulation of cerebral blood flow will be studied by inducing abrupt increases and decreases in inspired CO2. Partial pressure of carbon dioxide will be monitored in arterial blood and in blood taken from the confluent sinus together with cerebral venous outflow. The half-times of the changes in blood PCO2 and cerebral blood flow will be calculated graphically. The blood brain barrier will be altered to see if the lag occurs there. Differences in the lag times recorded before and after this treatment will give this information. To identify brain areas that control cerebral blood flow, stimulations and lesioning selected brain structures will be carried out.